As someone who has lived in the city, I'm actually fairly sympathetic to the idea that New Yorkers shouldn't be forced to cope with the exigent costs of the trial. The other day, Charles Komanoff at Streetsblog gave an idea of how much of a disruption the trial would actually be:

Assuming that the restrictions take away one-quarter of the carrying capacity of the affected streets (one-half for streets within the inner section), vehicles in the area can expect to spend 2,200 additional hours stuck in traffic each weekday. Scaled to a full year, that translates to $30 million in lost time for motorists, truckers, taxi riders and bus passengers.

A fair trial for KSM and the other alleged 9/11 conspirators is not optional. The symbolism of trying them close to Ground Zero is—and the administration should have more carefully assessed the potential costs of the trial to the city before it made the ultimate decision to try them there. That said, it may not just have been a matter of symbolism, the Southern District is where a number of cases have been tried. Ben Smithreports that Nicholas Valentine, the Republican Mayor of Newburgh in upstate NY, is "begging" for the trial because the federal money would help the town pay for its new courthouse.

Senator Lindsey Graham has also said that he plans to re-introduce a bill that would prevent the administration from trying the 9/11 conspirators in civilian court. Republican complaints about micromanaging the Commander-in-Chief's decisions during wartime don't apply to decisions made by a Democratic president.

There's also a potentially even more cynical motivation for the bill, however. Graham, a former JAG lawyer, is the Senate's expert on military law. He helped craft the revised military commissions, so he has to know that the prior commissions were ineffective, and that the new ones still might not be constitutional. Republicans have an interest in not revisiting the torture of terror suspects in open court, so preventing a civilian trial for KSM, depending on whether or not the commissions pass constitutional muster, could mean simply putting off any kind of trial indefinitely.